Abstract:

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Thermal stress, plastic slip deformation and accumulation of dislocations in shallow
trench isolation (STI) type ULSI devices when the temperature drops from 1000 し to room
temperature are analyzed by a crystal plasticity analysis cord. The results show that dislocation
accumulation takes place at the temperature range over 800 し, and the difference of 6 MPa in the
lattice friction stress at 1000 し!causes increase of dislocation density more than 1.6 times.
Dislocations generate and accumulate at the shoulder part of the device area and bottom corners of
the trench. Dislocations are categorized into two groups. In one group, dislocation lines are
mostly straight and parallel to the trench direction, and in the other group, dislocations make half
loop type structure. Possibilities for the suppression of dislocation accumulation through control
of lattice friction stress at high temperature region are discussed.

Abstract: In this study, we develop a multiscale crystal plasticity model that represents evolution of
dislocation structure on formation process of ultrafine-grained metal based both on dislocation
patterning and geometrically necessary dislocation accumulation. A computation on the processes of
ultrafine-graining, i.e., generation of dislocation cell and subgrain patterns, evolution of dense
dislocation walls, its transition to micro-bands and lamellar dislocation structure and formation of
subdivision surrounded by high angle boundaries, is performed by use of the present model.
Dislocation patterning depending on activity of slip systems is reproduced introducing slip rate of
each slip system into reaction-diffusion equations governing self-organization of dislocation structure
and increasing immobilizing rate of dislocation with activation of the secondary slip system. In
addition, we investigate the effect of active slip systems to the processes of fine-graining by using the
pseudo-three-dimensional model with twelve slip systems of FCC metal.

Abstract: The thermal effect has pronounced influence on deformation behavior of materials at nanoscale due to small length scale. In current paper, shear deformation of single crystal copper is simulated by molecular dynamics simulation, and special attention is paid to the thermal effect on the deformation behavior of material and mechanical response. The result shows that the plastic deformation of material during shear deformation is dominated by dislocation activities. Both the yield strength and shear strength have strong dependence on temperature due to thermal effect.

Abstract: By the measurement of creep curves and microstructure observation, an investigation has been made into the creep behaviors and microstructure evolution of a single crystal nickel-based superalloy containing 4.2%Re. Results show that the superalloy displays an obvious sensibility on the applied temperatures and stresses in the range of the applied temperatures and stresses. During the initial creep, the cubical g¢ phase in the alloy is transformed into an N-type rafted structure along the direction vertical to the applied stress axis. After crept up to fracture, the rafted g¢ phase in the region near fracture is transformed into a twisted configuration. The dislocation climbing over the rafted g¢ phase is considered to be the main deformation mechanism of the alloy during the steady creep state, and dislocations shear into the rafted g¢ phase is the main deformation mechanism of the alloy in the later stage of creep.

Abstract: The size dependent hardening in Al-4wt%Cu thin film on Si substrate has been investigated by the numerical calculation of indentation stress field and the observation of plastic zone microstructure of indented film. Distribution of internal stress predicted by triangular dislocation loop (TDL) model shows no size dependency with the different number of dislocations when the constant line density is assumed at the contact surface. TEM cross-sectional observation reveals that the plastic deformation is dominantly induced inside the film, and the growth of plastic zone is restricted at the interface of hard Si substrate. The size dependent hardening in soft film and hard substrate system is discussed from the change in dislocation density with respect to the plastic zone microstructure.

Abstract: Dislocation Dynamics (DD) simulations are used to study the evolution of a pre-specified dislocation structure under applied stresses and imposed boundary conditions. These simulations can handle realistic dislocation densities ranging from 1010 to 1014 m-2, and hence can be used to model plastic deformation and strain hardening in metals. In this paper we introduce the basic concepts of DD simulations and then present results from simulations in thin copper films and in bulk zirconium. In both cases, the effect of orientation on deformation behaviour is investigated. For the thin film simulations, rigid boundary conditions are used at film-substrate and film-passivation interfaces leading to dislocation accumulation, while periodic boundaries are used for bulk grains of Zr. We show that there is a clear correlation between strain hardening rate and the rate of increase of dislocation density.